Thermal-Hydraulic Challenges in Fast Reactor Design

Thermal-hydraulic challenges in the design of the following four Generation IV fast reactor concepts are presented: sodium \[sodium-cooled fast reactor (SFR)\], lead \[lead-cooled fast reactor (LFR)\], gas \[gas-cooled fast reactor (GFR)\], and liquid salt \[liquid salt-cooled fast reactor (LSFR)\]. The supercritical carbon dioxide Brayton cycle in indirect mode is the candidate power cycle for all coolants except gas, which is direct cycle. Thermal-hydraulic considerations must be closely integrated with neutronic analysis to properly control reactivity feedbacks, particularly that of the coolant density coefficient. The thermal-hydraulic performance of all reactors is compared to the sodium concept, which has superior performance because of the inherent properties of sodium. The chemical incompatibility of sodium with water and air remains a concern, should a steam generator tube or other sodium line leak. Challenges in steady-state operation, transient performance, shutdown heat removal, and loss-of-coolant-accident design accommodation in gas reactors are reviewed.